Gating system for flowable material and conveying apparatus including same

ABSTRACT

A gating system for controlling the flow of a flowable material through a passageway having an inlet and an outlet, the gating system includes: an inlet blade assembly between the passageway inlet and passageway outlet, the inlet blade assembly including an inlet blade and a drive for moving the inlet blade to open and closed positions with respect to the passageway; an outlet blade assembly between the inlet blade assembly and the passageway outlet, the outlet blade assembly including an outlet blade and a drive for moving the outlet blade to open and closed positions with respect to the passageway; and a control system that drives for moving the inlet blade to its closed position before moving the outlet blade to its closed position with respect to the passageway, and moves the outlet blade to its open position before moving the inlet blade to its open position.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a gating system for controlling theflow of a flowable material. The invention is particularly useful inconveying apparatus for conveying a flowable material, such as grains,sand, plastic particles and powders, etc., from a large container, suchas a silo or hopper, to another destination, such as a remotely-locatedstorage container. The invention is therefore described belowparticularly with respect to such an application, but it will beappreciated it could also be used in many other applications.

At the present time, flowable material is commonly conveyed from onedestination to another either by a mechanical conveyor, such as a rotaryfeeder, or by a pneumatic conveyer which conveys the material bypressurized air. Each has its advantages and disadvantages. For example,while mechanical feeders feed the material continuously, their feedingrate is very limited, and their contact with the flowable material, suchas grains, can be damaging. The pneumatic conveying systems feed thematerial in batches and/or continuously, generally occupy a large space,and require costly installations and gating systems particularly becauseof the need for good sealing in order to avoid high losses in thepressurized air used for conveying the flowable materials.

OBJECTS AND BRIEF SUMMARY OF THE PRESENT INVENTION

An object of the present invention is to provide a gating system havinga number of advantages over those used today, which make such gatingsystems particularly useful in pneumatic apparatus for conveyingflowable material. Another object of the invention is to provide animproved conveying apparatus including the novel gating system.

According to one aspect of the present invention, there is provided agating system for controlling the flow of a flowable material through apassageway having an inlet and an outlet, the gating system comprising:an inlet blade assembly between the passageway inlet and passagewayoutlet, the inlet blade assembly including an inlet blade and a drivefor moving the inlet blade to open and closed positions with respect tothe passageway; an outlet blade assembly between the inlet bladeassembly and the passageway outlet, the outlet blade assembly includingan outlet blade and a drive for moving the outlet blade to open andclosed positions with respect to the passageway; and a control systemfor controlling the drives for moving the inlet blade to its closedposition before moving the outlet blade to its closed position withrespect to the passageway, and for moving the outlet blade to its openposition before moving the inlet blade to its open position with respectto the passageway.

As will be described more particularly below, the provision of two bladeassemblies and there control as set forth above reduces the need forextremely reliable sealing in order to prevent undue loss of compressedair used in the pneumatic conveying operation.

According to further features in the preferred embodiments of theinvention described below, the outlet blade assembly includes a sealcooperable with the outlet blade when in its closed position to seal thepassageway and the inlet blade assembly therein. The seal may be aninflatable seal, in which case the control system would inflate the sealafter the outlet blade has been moved to its closed position, anddeflate the seal before the outlet blade is moved to its open position.This feature further reduces the possibility of losing compressed airduring the operation of the gating system.

According to further features in the described preferred embodiments,the inlet blade assembly includes a pair of open frame members betweenwhich the inlet blade is movable to its open and closed positions. Theopen frame member of the inlet blade assembly facing the outlet bladeassembly is interrupted to permit passage to the outlet blade assemblyof flowable material located between the two frame members of the inletblade assembly during the movement of the inlet blade to its closedposition.

According to still further features in the described preferredembodiments, the outlet blade assembly also includes a pair of framemembers between which the outlet blade is movable to its open and closedpositions. The open frame member of the outlet blade assembly proximalto the passageway outlet carries, on its surface facing the other openframe member of the outlet blade assembly, a plurality of jet cleaningnozzles controlled by the control system for discharging cleaning jetstowards the outlet blade to clean it during the opening and/or closingmovements of the outlet blade.

According to still further features in one described embodiment, theoutlet blade carries a plurality of jet cleaning nozzles controlled bythe control system for cleaning the open frame members of the outletblade assembly during the opening and/or closing movements of the outletblade.

According to another aspect of the present invention, there is providedconveying apparatus including a gating system as set forth above; acontainer for containing a quantity of flowable material and for feedingsame by gravity to the inlet of the passageway; a tank communicatingwith the outlet of the passageway; and a source of pressurized gas topressurize the tank and to convey the flowable material therein toanother destination; the control system also controlling the source ofpressurized gas to pressurize the tank only when the outlet blade of theoutlet blade assembly has been moved to its closed position.

According to a still further aspect of the present invention, there isprovided a conveying system wherein the conveying apparatus comprisestwo gating systems, each underlying a part of the container, and twotanks, each underlying one of the gating systems and communicating withthe source of pressurized gas; and wherein the control system controlsthe drives of the gating systems and the source of pressurized gas toalternatingly fill one tank with flowable material from the containervia its gating system, while pressurizing the other tank to convey itscontents to the another destination.

As will be described more particularly below, gating systems constructedin accordance with the foregoing features provide a number of importantadvantages which make them particularly useful for conveying flowablematerials, such as grain, from one location to another.

Further features and advantages of the invention will be apparent fromthe description below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 illustrates one type of conveying apparatus including a gatingsystem constructed in accordance with the present invention;

FIG. 2 is a schematical side elevational view of the gating systemincluded in the apparatus of FIG. 1;

FIG. 3 is a side elevational view only of the upper blade assembly atthe inlet of the passageway controlled by the gating system of FIG. 2;

FIG. 4 is a top plan view of the upper blade assembly of FIG. 3;

FIG. 5 is a bottom plan view of the upper blade assembly of FIG. 3;

FIG. 6 is a side elevational view of the lower blade assembly at theoutlet of the passageway controlled by the gating system;

FIG. 7 is a top plan view of the lower blade assembly of FIG. 6;

FIG. 8 is a top plan view of the blade in the lower blade assembly ofFIG. 6;

FIG. 9 is a bottom plan view of the lower blade assembly of FIG. 6;

FIG. 10 is an upper plan view of the lower open frame member in thelower blade assembly of FIG. 6;

FIG. 11 is a flow chart illustrating the overall operation of the gatingsystem of FIGS. 2-10 in the conveying apparatus of FIG. 1;

FIG. 12 illustrates a modification in the construction of the drives forthe blades in the gating system of FIGS. 1-1;

FIG. 13 illustrates another modification in the construction of thedrives;

FIG. 14 illustrates a modification in the construction of the blade inthe lower blade assembly at the outlet of the passageway controlled bythe gating system;

FIG. 15 is a top plan view of the blade illustrated in FIG. 14;

FIG. 16 is a front view of the blade illustrated in FIG. 14; and

FIG. 17 illustrates conveying apparatus including two gating systemsconstructed in accordance with the invention.

It is to be understood that the foregoing drawings, and the descriptionbelow, are provided primarily for purposes of facilitating understandingthe conceptual aspects of the invention and various possible embodimentsthereof, including what is presently considered to be a preferredembodiment. In the interest of clarity and brevity, no attempt is madeto provide more details than necessary to enable one skilled in the art,using routine skill and design, to understand and practice the describedinvention. It is to be further understood that the embodiments describedare for purposes of example only, and that the invention is capable ofbeing embodied in other forms and applications than described herein.

DESCRIPTION OF PREFERRED EMBODIMENTS

Overall Construction (FIGS. 1-10)

FIG. 1 illustrates one type of conveyor apparatus for which the presentinvention is particularly useful. The conveyor apparatus illustrated inFIG. 1 is for conveying flowable material, such as grain, from an inputsilo 2 to a remote silo 3 by pneumatic pressure supplied by a compressor4. The flowable material is gravity fed from silo 2 via a passageway 5into a buffering tank 6. Buffering tank 6 is provided with an inletvalve V₁ connecting compressor 4 to pressurize the tank, and with anoutlet valve V₂ for depressurizing the tank. Compressor 4, as well asthe two valves V₁, V₂, are controlled by control system 7, in the mannerto be described below, to periodically pressurize tank 6 in order toconvey its contents via a conduit 8 to the remote silo 3, and then todepressurize the tank in order to permit it to be refilled from theinput silo 2.

Buffering tank 6 further includes a pressure sensor S₁ for sensing thepressure within the tank, a low-level sensor S₂ for sensing the emptycondition of the tank, and a high-level sensor S₃ for sensing the fullcondition of the tank.

Buffering tank 6 is periodically refilled by gravity via a gatingsystem, generally designated 10, constructed in accordance with theinvention located within passageway 5 between tank 6 and the overlyinginput silo 2. Gating system 10, as more particularly illustrated inFIGS. 2-10. It is also controlled by control system 7 as moreparticularly described below with respect to the flow chart of FIG. 11.

As shown in FIG. 2, vertical passageway 5 receiving the gating system 10is defined by a plurality of spacer elements 11, 12, 13, 14, securedtogether by tie rods 15 between a pair of flanges 16, 17, between theinput silo 2 and buffering tank 6, respectively. A sealing gasket 18 islocated between flange 16 and the upper spacing member 11, and anothersealing gasket 19 is located between the lower sealing member 14 andflange 17.

As further shown in FIG. 2, gating system 10, located in verticalpassageway 5 between silo 2 and tank 6, includes an input bladeassembly, generally designated 20, between the passageway inlet 5 a andoutlet 5 b, and an outlet blade assembly, generally designated 30,between the inlet blade assembly 20 and the passageway outlet 5 b.

The inlet blade assembly 20 includes a pair of open frame members 21,22, fixed within passageway 5, and an inlet blade 23 movable between theopen frame members 21, 22 either to a closed position (shown in FIG. 2),or to an open position, with respect to passageway 5. Inlet blade 23 ismoved to its two positions via a drive including a cylinder 24 and apiston 25 movable therein and coupled by arm 26 coupled to the inletblade 23.

Similarly, the outlet or lower blade assembly 30 includes a pair of openframe members 31, 32, fixed in spaced relationship to each other withinvertical passageway 5, and an outlet blade 33 movable to open and closedpositions within the passageway by a drive including a cylinder 34 and apiston 35 movable therein and coupled by arm 36 to the outlet blade 33.

The construction of the inlet (higher) blade assembly 20 is moreparticularly illustrated in FIGS. 3-5; whereas the construction of theoutlet (lower) blade assembly 30 is more particularly illustrated inFIGS. 6-10.

As shown in FIGS. 3-5, the two open frame members 21, 22 of the inletblade assembly 20 are fixed within vertical passageway 5 by spacer 12.Both frame members, as well as the inlet blade 23 between them, are of arectangular (square) configuration, but it will be appreciated that theycould be of other configurations as well, e.g., a circularconfiguration. The upper open frame member 21 extends for the completecircumference (360°) of the frame member, whereas the lower frame member22 extends for only about 270° of its circumference, being open at oneside (right side, FIG. 5). The lower frame member 22 thus defines aspace 27 for flowable material to pass therethrough during the closingof the inlet blade 23, as will be described more particularly below.

The outlet (lower) blade assembly 30, as more particularly illustratedin FIGS. 6-10, is also of rectangular (square) configuration, as theinlet blade assembly 20, but could also be of a different configuration(e.g., circular) to correspond to that of the inlet blade assembly. Inthis case, both frame members 31, 32 extend for the complete (360°)circumference of the blade assembly. They are fixed in the outlet end 5b of vertical passageway 5 by spacer 13.

As shown in FIGS. 6 and 8, the upper surface of the outlet blade 33includes a sealing ring 37 located within an angular groove 37 a formedin the upper surface of blade 33. Sealing ring 37 may be normallydeflated to permit its blade 33 to move between the two open framemembers 31, 32, and inflatable when the blade is in its closed positionso as to engage the lower surface of the upper frame member 31 andthereby seal the space between blade 33 and frame member 31. Theinflation and deflation of sealing ring 37 is effected via an air port37 b (FIG. 6) and is controlled by control system 7 (FIG. 1). While seal37 is shown in FIG. 8 as being carried by blade 33, which therebyfacilitates its periodic replacement, it may also be carried by thelower surface of the upper frame member 31. Also, an inflatable seal isnot necessary, since the pressure applied to the tank during theconveying phase will press the lower blade, and its sealing ring 37,firmly against the underside of the upper frame member 31.

As shown particularly in FIG. 10, the upper surface of the lower openframe member 32 is formed with an annular array of openings 38 whichserve as jet cleaning nozzles directing air jets upwardly towards thelower surface of the upper frame member 31 to flush same of any clingingparticles during the opening and/or closing movements of the blade. Thepressurized air for nozzles 38 is supplied via air port 38 a controlledby control system 7 (FIG. 1).

The two drives, 24, 25 and 34, 35, respectively, for the two blades 23and 33, are housed within a housing 40 (FIG. 2) laterally of thevertical passageway 5 between the input silo 2 and the buffering tank 6.As shown in FIG. 2, housing 40 is secured laterally of passageway 5 bytie rods 15, and is sealed with respect to that passageway by gaskets 18and 19, as well as a further gasket 41 around an opening defined at oneside of the spacer elements 11, 12 and 13. In addition, preferablyanother seal 42 is carried by the outlet (lower) blade 33, engageablewith the lower frame member 32 when the outlet (lower) blade 33 is inits closed position (FIG. 2).

It will thus be seen that the interior of housing 40 is substantiallysealed from the interior of vertical passageway 5, particularly whenhigh air pressure is applied to buffering tank 6 as will be describedbelow. Nevertheless, housing 40 may be periodically air-flushed byhigh-pressure air applied via an inlet port 43 and discharged via anoutlet port 44.

The two drives for the two blade assemblies 20, 30 preferably includelimit switches defining the open and closed positions of theirrespective blades 23, 33. Thus, as shown in FIG. 2, cylinder 24 includesa limit switch 24 a engageable by its piston arm 26 in the open positionof its blade 23, and another limit switch 24 b engageable by arm 26 inthe closed position of its blade. Similar limits which are provided oncylinder 34 defining the open and closed positions of its blade 33. Onlylimit switch 34 a is seen in FIG. 2; the other limit switch may beembedded within seal 42.

In the construction illustrated in FIG. 2, the pistons 25, 35 arecoupled to their respective upper blade 23 and lower blade 33 by arms26, 36 extending laterally of the respective cylinder 24, 34.Accordingly, the cylinders would have to be provided with elongatedslots to accommodate these arms. Since the interior of housing 40 is notperfectly isolated from the flowable material, the elongated slotsformed in the cylinders 24, 34 are preferably covered by a displaceablecover which normally seals the respective slots but permits the lateralarms 26, 36 to move along the linear slots in the cylinders. As oneexample, the covers 45, 46 may be of a silicon rubber or otherelastomeric material formed with a slit having overlapping edges whichtend to seal the interior of the respective cylinder but permit thelateral arm 26, 36, to move there along for coupling the respectiveblade 23, 33, to the respective piston 25, 35.

Operation (FIG. 11) and Some Advantages

The operation of the apparatus illustrated in FIGS. 1-10 will now bedescribed particularly with reference to the flow chart of FIG. 11.

It will be assumed that the two blades 23, 33 of the two bladeassemblies 20, 30, are in their open positions, and that a batch of theflowable material has passed through vertical passageway 5 into thebuffering tank 6 as determined by the upper level sensor (S₃) in thetank. The flow chart illustrated in FIG. 11 describes a cycle ofoperation for conveying the contents of tank 6 via conduit 8 to theremote silo 3, and then for refilling tank 6 with another batch of theflowable material from the input silo 2.

Thus, the first operation illustrated in the flow chart of FIG. 11 is toclose the inlet (upper) blade 23. For this purpose, control system 7actuates the drive (piston 25 movable within cylinder 24) of the upperblade assembly 20 to move its blade 23 to its closed position (block51). During this closing movement of the upper blade 23, any material inthe space between its frame members 21, 22 would be pushed by theclosing blade to fall through its lower frame member 22 and through theopen lower blade assembly 30 into the tank 6. During the final closingmovement of blade 23 such material would be pushed into space 27 at theend of its lower frame member 22.

After the upper blade 23 has been fully closed, control system 7 iscontrolled to actuate nozzles 38 (block 52), and then to actuate thedrive (piston 35 movable within cylinder 34) to move the lower blade 33to its closed position (block 52). Thus, during this closing movement ofthe lower blade 33, the air nozzles 38 in the lower frame member 32 ofthe lower blade assembly 30 are activated with air to flush away anymaterial clinging to the underside of the upper frame member 31 of thelower blade assembly 30 and to permit such material to fall into tank 6(block 53). This better assures that seal 37 will remain clean.

During the closing movements of the lower blade 33, its seal 37 is in adeflated condition to facilitate this movement of the blade. As soon asthe lower blade 33 has reached its closed position, its inlet seal 37 isinflated to thereby firmly engage the upper frame member 31 of the lowergate assembly 30, and thereby to seal this part of the passageway 5(block 54). As indicated earlier seal 37 need not be an inflatable onesince the pressure applied by tank 6 to the lower blade 33 will pressthat blade, and its seal 37, against the underside of frame member 31 toeffect a good seal. Thus, an important advantage of the novel gatingsystem is the greater the system pressure, the better the seal.

When the tower blade 33 is thus firmly closed, seal 42 prevents anyleakage of pressure from tank 6 to the interior of housing 40. Thisreduces the necessity of providing housing 40 with a good seal.

At this time, control system 7 actuates compressor 4 to apply highpressure via valve V2 to the interior of tank 6, and thereby to transferits contents via conduit 8 to the remote silo 3 (block 55). Thiscontinues until the tank is emptied, as indicated by the low-levelsensor S₂ within the tank (block 56).

As soon as the tank has thus been emptied, control system 7 interruptsthe pressure supplied by compressor 4 to the tank (block 57); deflatesseal 37 carried by the lower blade 33 (block 58); drives the lower blade33 to its open position (block 59); and then drives the upper blade 23to its open position (block 60).

With both blades 23 and 33 thus in their open positions, tank 6 ispermitted to refill by gravity until its upper level sensor S₃ isactuated (block 61) to thereby start a new cycle for conveying thecontents of tank 6 to the remote silo 3 and then for refilling the tank.

It will thus be seen that the novel gating system 10, including the twoblades 23, 33, provides a number of important advantages over gatingsystems previously used in such conveying apparatus. Thus, when closingthe gating system 10 within passageway 5, the upper blade 23 is closedfirst, i.e., while the lower blade is still open, whereby the movementof the lower blade to its open position is effected in a relativelyclean environment. In addition, when the high pressure is applied totank 6, seal 37 of the lower blade assembly 30 substantially isolateseverything above the lower blade 33 from the high pressure. Thus, asdistinguished from other gating systems which are limited as to thepressure they can tolerate, the gating system of the present inventionis virtually unlimited in this respect, since the greater the systempressure, the better the seal. After the contents of tank 6 have beenconveyed to the remote silo 3 by the high pressure applied to the tankand the high pressure has been released, only then is the gating systemactuated to its open position. This is done by first opening the lowerblade 33, effected in a relatively clean environment, and then openingthe upper blade 23 to permit tank 6 to be refilled with a new batch ofthe flowable material.

The new gating system is thus simple, reliable, less costly,considerably more compact, and/or simpler to maintain, as compared togating systems of other constructions. These advantages make the novelgating system particularly useful in pneumatic conveying apparatus and,in most cases, obviates the need for complex constructions andexcavations heretofore required in conveyance sites.

Some Variations and Modifications

FIG. 12 illustrates a variation with respect to the drives for the twoblade assemblies, therein designated 120, 130, respectively. Thus, thedrives illustrated in FIG. 12 are also constituted of pistons 125, 135,movable within cylinders 124, 134, respectively, and coupled by couplingmembers 126, 136, to the blade 123, 133, of the respective bladeassembly. However, in the construction illustrated in FIG. 12, thecylinders 124, 134, are located outside of the housing 140, and theirrespective pistons 125, 135, are coupled by piston stems 126, 136, tothe respective blades 123, 133. Thus, the cylinders 124, 134 aresubstantially isolated from the flowable material which may penetrateinto housing 140, and therefore do not require the special sealingarrangements as described above with respect to FIGS. 2-10. Housing 140,however, is preferably also periodically flushable of any materialaccumulating therein via an inlet flushing port 143 and an outletflushing 144.

FIG. 13 illustrates a construction similar to that of FIGS. 2-10, exceptthat the drives for the upper and lower blades 23, 33, are screw drives,rather than piston-cylinder drives. Thus, as shown in FIG. 13, the drivefor the upper blade 23 includes a screw 224 rotated by a motor M₁ todrive a nut 225 coupled by arm 226 to the upper blade 23; whereas thedrive for the lower blade 33 includes another screw 234 driven by motorM₂ for driving a nut 235 coupled by arm 236 to the lower blade 233. Insubstantially all other respects, the construction and operation of thearrangement illustrated in FIG. 13 are substantially the same asdescribed above with respect to FIGS. 2-11.

FIGS. 14-16 illustrate several modifications in the construction of thelower blade assembly, therein designated 330.

One such modification is that the upper surface of the lower open framemember 332 is upwardly inclined, as shown at 332 a, at the end thereofengaged by the lower blade 333 at the end of the travel of the blade toits closed position, such that inclined surface 332 a tends to enhancethe seal produced by seal 337 with respect to frame member 331 in theclosed condition of the lower blade 333. As shown by arrow 334, there isa sufficient space between the upper frame member 331 and the seal 337on the lower blade to avoid contact with the seal during the opening andclosing movements of the blade. This feature also avoids the need for aninflatable seal.

Another modification included in the lower blade assembly 330illustrated in FIGS. 14-16 is the provision of a plurality of air jetnozzles, generally designated 339, along the leading edge of the lowerblade 333 as it moves towards its closed position. Thus, as shown inparticularly in FIG. 16, nozzles 339 include a lower linear array ofnozzles 339 a oriented to direct air jets against the upper surface ofthe lower frame member 332 to free those surfaces of clinging material,and an upper linear array of nozzles 339 b oriented to direct air jetsagainst the lower surface of the upper frame member 331 during theclosing movements of the lower blade 333. These jet nozzles are suppliedby pressurized air via channels 339 c terminating in inlet port 339 dformed in the lower blade 333.

In all other respects, the gating system illustrated in FIGS. 14-16 isconstructed and operates in the same manner as described above.

The foregoing constructions illustrate a batch process, wherein a batchof the flowable material is discharged from the input silo 2 into tank 6and then conveyed by pneumatic pressure to the remote silo 3 via conduit8. Accordingly, each conveying period is interrupted by a non-conveyingperiod during which the tank 6 is filled from the silo.

FIG. 17 illustrates apparatus wherein the delay between the batches isminimized by providing two tanks 306 a, 306 b each underlying a gatingsystem 310 a, 310 b both supplied from different portions of a commonsilo 302. Thus, the control system 307 in the apparatus of FIG. 17controls the drives in the two gating systems 310 a, 310 b, as well asthe compressor 304 and the valves V₁, V₂, to alternatingly fill one tankwith the flowable material from silo 2 via its respective gating system,while pressurizing the other tank to convey its contents to the remotesilo 303. Thus, the throughput of such an apparatus is substantiallydoubled.

While the invention has been described with respect to several preferredembodiments, it will be appreciated that these are set forth merely forpurposes of example, and that many of the described features could beused without others, and many further variations, modifications andapplications of the invention may be made.

1. A gating system for controlling the flow of a flowable materialthrough a passageway having an inlet and an outlet, said gating systemcomprising: an inlet blade assembly between said passageway inlet andpassageway outlet, said inlet blade assembly including an inlet bladeand a drive for moving said inlet blade to open and closed positionswith respect to said passageway; an outlet blade assembly between saidinlet blade assembly and said passageway outlet, said outlet bladeassembly including an outlet blade and a drive for moving said outletblade to open and closed positions with respect to said passageway; anda control system for controlling said drives for moving said inlet bladeto its closed position before moving said outlet blade to its closedposition with respect to said passageway, and for moving said outletblade to its open position before moving said inlet blade to its openposition with respect to said passageway.
 2. The gating system accordingto claim 1, wherein said outlet blade assembly includes a sealcooperable with said outlet blade when in its closed position to sealsaid passageway and said inlet blade assembly therein.
 3. The gatingsystem according to claim 2, wherein said seal is carried by said outletblade.
 4. The gating system according to claim 2, wherein said seal isan inflatable seal; and wherein said control system inflates said sealafter the outlet blade has been moved to its closed position, anddeflates said seal before the outlet blade is moved to its openposition.
 5. The gating system according to claim 1, wherein said inletblade assembly includes a pair of open frame members between which saidinlet blade is movable to its open and closed positions.
 6. The gatingsystem according to claim 5, wherein the open frame member of the inletblade assembly facing the outlet blade assembly is interrupted to permitpassage to the outlet blade assembly of flowable material locatedbetween the two frame members of the inlet blade assembly during themovement of the inlet blade to its closed position.
 7. The gating systemaccording to claim 1, wherein said outlet blade assembly includes a pairof frame members between which said outlet blade is movable to its openand closed positions.
 8. The gating system according to claim 7, whereinthe open frame member of the outlet blade assembly proximal to thepassageway outlet carries, on its surface facing the other open framemember of the outlet blade assembly, a plurality of jet cleaning nozzlescontrolled by said control system for discharging cleaning jets towardsthe outlet blade to clean it during the opening and/or closing movementsof the outlet blade.
 9. The gating system according to claim 7, whereinsaid outlet blade carries a plurality of jet cleaning nozzles controlledby said control system for cleaning said open frame members of theoutlet blade assembly during the opening and/or closing movements of theoutlet blade.
 10. The gating system according to claim 7, wherein theopen frame member of the outlet blade assembly facing away from theinlet blade assembly is formed with an inclined surface to move theoutlet blade towards the open frame member of the outlet blade assemblyfacing the inlet blade assembly during the end movement of the outletblade to its closed position.
 11. The gating system according to claim1, wherein said drives are enclosed in a common housing; and whereinsaid housing includes an air inlet and an air outlet for air flushingthe interior of said housing.
 12. The gating system according to claim1, wherein each of said drives includes a drive member, a driven member,and an arm extending through an elongated, sealed slot in said drivemember and coupling said driven member to its respective blade.
 13. Thegating system according to claim 12, wherein in each of said drives,said drive member is a cylinder, and said driven member is a pistonmovable therein.
 14. The gating system according to claim 12, wherein ineach of said drives, said drive member is a screw, and said drivenmember is a nut movable thereon.
 15. The gating system according toclaim 1, wherein said passageway is a vertical passageway, said inlet anoutlet blades are horizontal blades, and said flowable material flowsthrough said passageway by gravity, whereby said inlet blade assembly isan upper blade assembly, and said outlet blade assembly is a lower bladeassembly underlying said upper blade assembly.
 16. The gating systemaccording to claim 15, wherein said passageway outlet communicates witha tank of said flowable material; and wherein said tank includes asource of pressurized gas for conveying the flowable material from saidtank to another destination.
 17. The gating system according to claim16, wherein said control system also controls said source of pressurizedgas to pressurize said tank only when said outlet blade of the outletblade assembly has been moved to its closed position.
 18. Conveyingapparatus for conveying a flowable material, said conveying apparatuscomprising: a gating system according to claim 1; a container forcontaining a quantity of flowable material and for feeding same bygravity to the inlet of said passageway; a tank communicating with theoutlet of said passageway; and a source of pressurized gas to pressurizesaid tank and to convey the flowable material therein to anotherdestination; said control system also controlling said source ofpressurized gas to pressurize said tank only when the outlet blade ofthe outlet blade assembly has been moved to its closed position.
 19. Theconveying apparatus according to claim 18, wherein the apparatuscomprises two gating systems, each underlying a part of said container,and two tanks, each underlying one of said gating systems andcommunicating with said source of pressurized gas; and wherein saidcontrol system controls said drives of the gating systems and saidsource of pressurized gas to alternatingly fill one tank with flowablematerial from said container via its gating system, while pressurizingthe other tank to convey its contents to said another destination.